Reusable code, faster time-to-market, reduced cost, and native app like performance are some of the prominent reasons behind acceptance of cross-platform app development.
Hybrid apps are often looked on as a cross platform app development solution. They are essentially small websites that runs under a native wrapper. And therefore, instead of serving as a web page, hybrid apps work as a standalone application.
Ionic is HTML5 framework, meant for hybrid mobile app development. Hybrid apps get the better of native apps, in terms of support to multiple platforms, access to third party code, and less time-to-market.